1. Field of Invention
The invention relates to an ink cartridge to be used in printing apparatuses, such as printers, copy machines, and facsimile machines. More particularly, the invention pertains to an ink cartridge wherein detection accuracy of an ink remaining amount in the ink cartridge using an optical device can be improved.
2. Description of Related Art
There has been provided ink cartridges, used in printers or the like, that are structured so that ink level in the ink cartridges can be detected using an optical device. In the ink cartridge of this type, generally, ink is stored in a light-permeable case. The ink level is detected through the use of change in an amount of reflected light caused in accordance with the ink level, by which light is irradiated into the ink cartridge from a light source.
FIGS. 16A and 16B show a principle of detection of the presence or absence of ink in a conventional ink cartridge 200. As shown in FIGS. 16A and 16B, the ink cartridge 200 is molded using a light-permeable material (e.g. resin materials, such as polypropylene), and includes a main ink tank 203 that accommodates therein a foam (porous material) 202 capable of impregnating ink 201 and a sub-ink tank 205 to which light is applied from an ink sensor 204. The ink 201 is stored in both main and sub-ink tanks 203, 205. An ink jet head 207 is connected to the bottom of the ink cartridge 200 via an ink supply hole 206. The ink 201 is supplied from the ink cartridge 200 through the ink supply hole 206 and is ejected from the ink jet head 207. As a result, an image can be obtained on a recording medium.
In the ink cartridge 200, first, the ink 201 in the main ink tank 203 is gradually consumed (see FIG. 16A). After the ink 201 in the main ink tank 203 nearly runs out, the ink 201 in the sub-ink tank 205 is used (see FIG. 16B). The ink sensor 204 includes a light-emitting device 204a that irradiates infrared light toward the ink cartridge 200 and a photoreceptor device 204b that receives light reflected from the ink cartridge 200. The ink sensor 204 is disposed so as to be able to irradiate the infrared light toward the sub-ink tank 205.
As shown in FIG. 16A, when the ink cartridge 200 contains a large amount of ink (when the ink cartridge 200 contains the ink 201 in both the main and sub-ink tanks 203, 205), infrared light irradiated from the light-emitting device 204a of the ink sensor 204 (an optical path a1) travels in the ink cartridge 200 in a direction indicated with an optical path a2 while permeating the ink 201, because a refractive index of the material forming the ink cartridge 200 is close to a refractive index of the ink 201. Therefore, the infrared light is absorbed by the ink 201, so that an extremely small amount of the light is to be reflected from the inside of the ink cartridge 200 toward the photoreceptor device 204b in the ink sensor 204. Even when the photoreceptor device 204b receives such the amount of the reflected light, it is not determined that the ink is absent.
As opposed to this, as shown in FIG. 16B when the ink 201 is absent at the upper area of the sub-ink tank 205 of the ink cartridge 200, the infrared light irradiated from the light-emitting device 204a in the ink sensor 204 (an optical path b1) is reflected at a phase boundary between air 208 and an inner surface of an outer wall of the sub-ink tank 205 (an optical path b2), because the refractive index of the material forming the ink cartridge 200 is different from a refractive index of the air 208. Accordingly, a large amount of the light is reflected from the inside of the ink cartridge 200 toward the photoreceptor device 204b in the ink sensor 204. Accordingly, the photoreceptor device 204b receives the large amount of the reflected light, so that it is determined that the ink is absent.
As described above, the amount of the light to be reflected from the ink cartridge 200 changes in accordance with the presence or absence of the ink 201 at a predetermined level in the sub-ink tank 205. Therefore, a remaining amount of the ink 201 in the ink cartridge 200 can be detected by which a difference of the reflected light amount between the presence of the ink 201 and the absence of the ink 201 is detected using the photoreceptor device 204b in the ink sensor 204.
When the ink cartridge 200 contains a certain level of the ink 201 (when the level of ink 201 in the sub-ink tank 205 is up to the upper area of the sub-ink tank 205 although the ink 201 in the main ink tank 203 almost runs out (not shown)), the ink 201 is not absorbed in the foam 202. Therefore, infrared light irradiated from the light-emitting device 204a in the ink sensor 204 (an optical path a1) is reflected by the inner wall of the main ink tank 203 or the foam 202 (an optical path a3).
In this case, when the ink cartridge 200 contains intensely colored ink, such as black and cyan ink, a certain amount of the infrared light irradiated from the light-emitting device 204a in the ink sensor 204 (the optical path a1) is absorbed by the foam 202. Thus, an amount of reflected light that cannot be determined as the absence of ink, is reflected from the ink cartridge 200 toward the photoreceptor device 204b in the ink sensor 204.
However, when the ink cartridge 200 contains light-colored ink, such as yellow and magenta ink, a problem occurs that an amount of ink remaining in the ink cartridge 200 cannot be correctly detected. That is, the infrared light is hardly absorbed by light-colored ink, so that the infrared light that travels in the ink cartridge 200 containing the light-colored ink is reflected by the foam 202. Thus, the photoreceptor device 204b would receive a large amount of the reflected light (the optical path a3 in FIG. 16A) though the ink cartridge 200 contains the ink 201 in both main and sub-ink tanks 203, 205. Therefore, the difference of the reflected light amount between the presence and the absence of the ink 201 at the predetermined level in the sub-ink tank 205 is small, so that the amount of the ink 201 remaining in the ink cartridge 200 cannot be precisely detected.